In the field of industrial abrasives, it is a well-known technique to use as abrasive filaments which are made of a synthetic resin and abrasive grains mixed and dispersed in the synthetic resin.
As synthetic resins for abrasive filaments, polyamides such as nylon 6, nylon 66 and their copolymers are used primarily. Besides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and their copolymers as well as their mixtures are also employed.
In general, a mixture of one or more of such synthetic resins and one or more kinds of various abrasive grains is formed into filaments. The filaments are then bound together to use same as an abrasive brush.
Japanese Patent Laid-Open No. 76279/1986 discloses abrasive bristles composed of nylon 610 and abrasive grains. Japanese Patent Laid-Open No. 224268/1984 discloses abrasive monofilaments which are composed of PBT as a main component, a small amount of a polyamide, and abrasive grains. Further, Japanese Patent Publication No. 1146/1985 discloses a composition with improved cutting and polishing ability, which is formed of a thermoplastic resin selected from polyamides and polyesters, a small amount of an ethylene-vinyl acetate copolymer and abrasive grains.
When a metal surface is polished by means of abrasive filaments, the polishing work is performed while feeding warm water or an acidic warm water to the metal surface so as to eliminate resulting frictional heat and maintain the metal surface clean.
Conventional abrasive filaments made of a polyamide as a principal component however absorb water due to the inherent water absorption property of the polyamide in the course of polishing work, so that they are caused to swell. As a result, they are softened to reduce their abrasiveness. In particular, they are prone to deterioration with an acidic warm water so that the percentage of broken filaments (broken loss percentage) increases. As has been mentioned above, polyamide-base abrasive filaments are accompanied by drawbacks that their abrasiveness is reduced to a considerable extent under ordinary polishing work conditions and their durability is also inferior.
It is hence necessary to perform such a cumbersome operation that in accordance with quality and performance changes of such polyamide-base abrasive filaments in the course of polishing work, the revolutionary speed of the abrasive brush is increased or the pressing force is increased to enhance the abrasiveness.
On the other hand, polyester-base abrasive filaments have better waterproofness compared with polyamide-base abrasive filaments. Abrasive filaments making use of PET involve problems that their stiffness is too high to give high abrasiveness and their durability is inferior because PET is hydrolyzed and becomes brittle when used for a long period of time. Although abrasive filaments making use of PBT have suitable stiffness and high abrasiveness, but they are accompanied by problems that they have inferior flexing fatigue resistance and tend to be flattened, they are hence also inferior in durability and their performance as an abrasive is reduced very fast.